ASYNC and AWAIT keyword in ASP.NET Web API : 

Synchronous (Sync) and Asynchronous (Async) programming are two different approaches to handle operations and execution. 

The Async and Await keywords are used to write asynchronous code, allowing you to perform non-blocking operations and improve the scalability and responsiveness of your application. 

Synchronous and Asynchronous Programming: 

In synchronous programming, each operation is executed one after another, blocking the execution until the operation completes. 

Asynchronous programming allows multiple operations to be executed concurrently without blocking the main thread of execution. This approach is beneficial for long-running operations. 

async Keyword:  

The async keyword is used to define a method as asynchronous. When a method is marked as async, it can utilize the await keyword to asynchronously wait for the completion of other asynchronous operations.  

This allows the method to be non-blocking, allowing the server to process other requests while waiting for the operation to complete. 

await Keyword: 

The await keyword is used within an async method to await the completion of an asynchronous operation.  

When await is used, the execution of the method is paused, and the control is returned to the calling code until the awaited operation completes.  

By combining async and await, we can write asynchronous code in a more readable and structured manner.  

Here is a sample example for async and await keyword:

public class SampleController : ApiController 
{ 

    [HttpGet] 

    public async Task<IHttpActionResult> Get() 

    { 
        try 
        { 
            // Perform asynchronous operations 
            var result = await SomeAsyncOperation(); 
            // Return the result 
            return Ok(result); 
        } 
        catch (Exception ex) 
        { 
            // Handle the exception 
            return InternalServerError(ex); 
        } 
    } 
    private async Task<string> SomeAsyncOperation() 
    { 
        await Task.Delay(1000); // Simulate a delay of 1 second 
        return "Async operation completed!"; 
    } 
} 

Output: 

Async operation completed! 

In this example we have a SampleController with a single Get action method. 

The Get action is marked as async, indicating that it is an asynchronous operation. 

Inside the Get action, we call the SomeAsyncOperation method asynchronously using await.  

This example demonstrates how you can use async and await in an ASP.NET Web API program to handle asynchronous operations to improve the responsiveness and scalability of your application. 

Pros: 

Scalability: It allows the server to handle multiple requests concurrently. It efficiently utilizes server resources and reduce the chances of blocking the main thread. 

Responsiveness: This operations prevent the main thread from being blocked while waiting for I/O operations to complete. This ensures that your Web API remains responsive and continue processing other tasks while waiting for the operation to finish. 

Improved Performance: Asynchronous code reduces the time spent waiting for I/O operations, such as network requests or database queries, leading to improved performance and reduce the time. 

Cons: 

Increased Complexity: Asynchronous programming introduces additional complexity compared to synchronous code. It requires a good understanding of asynchronous patterns to ensure correct behavior and avoid issues. 

Debugging Challenges: Debugging asynchronous code can be more complex than synchronous code. Exceptions or errors may occur in different contexts or at different points in the code execution flow, making debugging more challenging. 

Overall, async and await can greatly enhance the scalability, performance, and responsiveness of your ASP.NET Web API application.